As application scenarios increase, ever increasing data transmission requirements make load of wireless networks become increasingly heavy. Wireless networks are improved and upgraded in many technological aspects. Among these technologies, a simplest and most direct manner is to increase spectrum resources. Frequency spectrums are strictly controlled by a frequency spectrum management organization, and frequency spectrums obtained in a manner of buying a license can hardly exist continuously; therefore, a technology of using spectrum resource fragments is required to increase a data transmission peak rate. A wireless device can use a free spectrum provided that the wireless device satisfies a power limit. However, data transmission in wireless communications usually requires a specific signal-to-noise ratio, and a free frequency spectrum may be used by some devices at any time; therefore, a technology of using spectrum resource fragments is also required for communication using a free frequency spectrum to increase a data transmission peak rate.
Currently, in daily life, a contradiction between rapidly growing data transmission and bandwidth of wireless communications increasingly deepens. Meanwhile, the trend that wireless spectrum resources are fragmented and dispersed further increases difficulty in transmission of a large amount of data. To fully utilize spectrum resources and satisfy increasing data transmission requirements, a carrier aggregation technology emerges, where this technology can properly resolve the foregoing problem by using spectrum resource fragments.
Conceptually, the carrier aggregation technology is to aggregate two or more component carriers to satisfy a requirement of a higher bandwidth and a higher data transmission rate. Carrier aggregation may be classified into continuous carrier aggregation and non-continuous carrier aggregation according to an extent to which spectrum resources are fragmented, as shown in FIG. 1.
In another aspect, network resources bearing data transmission are limited. Because the 802.11 standard is based on a carrier sense multiple access with collision avoidance (CSMA/CA, Carrier Sense Multiple Access/Collision Avoidance) mechanism, a quality of service (QoS) problem may occur as long as a case in which a network resource is contended for exists. First, because a data transmission volume increases and data services are classified in a more detailed manner, higher requirements are imposed on transmission resource allocation, a transmission latency, a data packet loss rate, and a delay variation, as shown in FIG. 2. Second, total transmission resources are limited; if a service of a specific type occupies more transmission resources for transmitting data, less transmission resources are available for another service to transmit data. Therefore, a higher requirement is also imposed on planning and allocation of transmission resources for various services on an 802.11 network.
In an existing mechanism of the 802.11 standard, channel bandwidth is divided into a primary component carrier and a secondary component carrier to increase signal transmission bandwidth, thereby improving a data transmission peak rate. As shown in FIG. 3, a 40 MHz primary component carrier includes a 20 MHz primary component carrier and a 20 MHz secondary component carrier, an 80 MHz primary component carrier includes a 40 MHz primary component carrier and a 40 MHz secondary component carrier, and a 160 MHz primary component carrier (not shown in the figure) includes an 80 MHz primary component carrier and an 80 MHz secondary component carrier, and so on. The mechanism in the 802.11 standard is similar to carrier aggregation; however, in this mechanism, contention-based access to a carrier is needed. Contention-based access to a carrier is performed in a sequence of a primary component carrier, a 20 MHz secondary component carrier, a 40 MHz secondary component carrier, and an 80 MHz secondary component carrier. According to this sequence, an access point (AP) or user equipment contends for a next carrier only when a previous carrier in the sequence is allowed to be accessed and used, and finally, carriers allowed to be accessed are combined together to form a channel with a high bandwidth to transmit data.
In the mechanism of contention-based access to a carrier that is performed according to priorities, if an AP or user equipment fails in contending for a carrier with a high priority, the AP or the user equipment gives up contending for a carrier with a low priority. As a result, a carrier with a lower priority is not fully used, load of carriers is not balanced, and a utilization rate of carriers with a low priority is reduced.